You are not a Void Knight, you mastered into Paladin. That’s why you can’t get Anomaly for Void Knight because its a level 30 skill.
Both Forge Guard and Void Knight passive trees stop at their level 20 talents.
Respeccing your mastery is the only thing you cant do in LE, its a permanent choice. So you have to create a new char if you wanna play a build with Anomaly.